Glutathione has a long history for the treatment of chronic liver disease by intravenous injection. This study demonstrates a therapeutic effect of glutathione by oral administration in patients with NAFLD. The primary outcome of this study was a change in ALT levels. The 29 patients who were treated with oral administration of glutathione (300 mg/day) for 4 months showed a reduction in ALT levels as well as reductions in triglycerides, NEFA, and ferritin levels. The findings of the current study suggest the beneficial effects of glutathione by oral administration for NAFLD patients. It is thought that glutathione is degraded into amino acids during digestion and absorption processes. Orally administered glutathione is suggested to serve as a source of amino acids in the synthesis of endogenous glutathione. Supplementation of large doses of glycine and serine, precursors of glutathione, can attenuate NAFLD in human and animal models [18, 19]. In the current study, the dose of glutathione was 300 mg/day. The amount of cysteine potentially released from 300 mg of glutathione is less than 120 mg, the amount that can be obtained from 10 to 20 g of meat or 100 mL of milk. It is, therefore, very unlikely that the current dose of orally administered glutathione attenuates the pathogenesis of NAFLD via an amino acid source for glutathione synthesis.
It is reported that the level of the protein-bound form of glutathione increases 1–2 h after ingestion of glutathione, which suggests that orally administered glutathione is absorbed into the blood . This protein-bound glutathione may be deposited in the liver, attenuating hepatitis.
The levels of protein-bound glutathione were reported to return to baseline levels after an overnight fast . In the current study, we found that the baseline level of the protein-bound form of glutathione significantly decreased after an overnight fast following 4 months of glutathione administration, especially in ALT responders. The levels of protein-bound glutathione in patients in the current study were considerably higher than those of healthy volunteers in previous studies  estimated using the same method. Glutathione treatment also decreased protein-bound glutathione to normal baseline levels. These findings suggest that oral administration of glutathione may increase the incorporation of protein-bound glutathione into the liver or decrease the pathological excretion of glutathione from the liver.
NAFLD is a complex disease. Its pathogenesis is thought to involve various factors, including insulin resistance, lipotoxicity, gut/nutrient-derived signals, adipocytokines, oxidative stress, and genetic factors. Dyslipidemia has been reported in 20–80% of patients with NAFLD . Our previously study revealed that orally administrated glutathione accelerates fatty acid utilization by upregulating levels of the protein peroxisome proliferator-activated receptor-γ coactivator-1α and mitochondrial DNA with reduced plasma NEFA levels . The current study also revealed that 24 (82.8%) of our patients had dyslipidemia, and glutathione treatment reduced triglyceride and NEFA levels significantly.
Increases in ferritin and body iron stores have been detected frequently in NAFLD patients [22, 23]. Ferritin and iron can promote the development of NAFLD through oxidative stress . Results from the PIVENS trial showed that oral administration of the anti-oxidant vitamin E improved liver dysfunction and the pathological conditions of NASH . However, long-term treatment with vitamin E has been associated with increases in all-cause mortality and the risk for prostate cancer [25,26,27], suggesting the need to evaluate the efficacy and safety of this agent. In the current study, glutathione treatment significantly decreased ferritin levels, but the mechanism behind the decrease remains unclear. Glutathione is thought to ameliorate hyperferritinemia and oxidative stress, and to have therapeutic effects in patients with NAFLD.
Liver fat was non-invasively assessed using VCTE with CAP. A meta-analysis found that CAP has good sensitivity and specificity for detecting liver fat . CAP values in our study tended to decrease in all patients and significantly decreased in ALT responders following 4 months of glutathione treatment. Although the relationship between histologic improvement of hepatic steatosis and the reduction of CAP values has not yet been determined, glutathione may reduce hepatic steatosis.
We also investigated the patient factors associated with the therapeutic effects of glutathione. We found that HDL cholesterol and LDL cholesterol levels were higher and HbA1c levels lower in ALT responders than in non-responders. Although the percentage of patients using statins did not differ significantly between the two groups, the percentage tended to be lower in ALT responders than in ALT non-responders. While it can be nothing more than speculation because of the small sample size, patients who showed therapeutic effects following glutathione treatment appeared to be younger and did not have diabetes or had mild diabetes.
Three patients withdrew from the study because of fatigue, elevated blood pressure, and a rash. In ALT responders, HbA1c levels increased and HDL cholesterol levels decreased after glutathione treatment. A study of 6522 patients found that 24 (0.4%) had experienced adverse reactions, the most frequent being anorexia, nausea, vomiting, and rash . Although administration of glutathione may have been associated with a rash in one patient in the current study, the causal associations between glutathione and other adverse effects are unclear.
This study had some limitations. First, our study was a single-arm study without a control group. Second, the study was limited by the small sample size and the short treatment period (4 months). Third, as the pathological conditions of the patients were not evaluated by liver biopsy, incorporation of orally administered glutathione in the liver was not confirmed. Fourth, a number of patients withdrew from the study but no causal association can be determined.